JBossWS-Native 3.1.1 simply didn't support that policy assertion. You need to use a more recent JBossWS / AS versions.
If you don't want to update the stack on AS 5 or 6, you could just download JBoss AS 6 M4 which comes with JBossWS-CXF 3.4.0.Beta1. That supports for sure all the most common policy assertions.